The present invention relates generally to determining the perfusion efficiency factor of animal tissue, and more particularly to a method and an apparatus for percutaneously determining this factor.
The term "perfusion efficiency factor" as used in the present disclosure is intended to designate a physiological value which is determined by the degree or rate of perfusion (in the case of organs the blood circulation in ml/unit weight/time) and the local concentration of the substance supplied to a given locus by the perfusion (herein called the indicator concentration). A high efficiency of perfusion is obtained if the indicator substance is so distributed in the organ by a perfusion which should be as low as possible, that its concentration corresponds to the existing physiological requirements.
It is already known to determine the blood circulation of an organ at the surface thereof by measuring the thermal conductivity at the surface of the organ. This thermal conductivity depends upon the thermal conductivity of the tissue and the flow of blood through it, that is upon the rate of perfusion. The prior art has proposed either measuring the temperature difference between two thermal sensors of which one is heated at a constant temperature, or providing two measuring surfaces between which a constant temperature differential is produced and the amount of heat required for maintaining the temperature differential is then measured. This latter approach utilizes an annular diathermically heated surface, and a second measuring surface which is located at the center of the space surrounded by this first surface. It is also known to use other approaches, for instance to measure the H.sub.2 clearance, or by measuring the radioactive clearance.
However, the perfusion efficiency factor cannot be determined with these prior art approaches, because the results which are derived with them are not correlated with the indicator concentration.
Measurement of the indicator concentration at any particular locus in a percutaneous manner is also known from the prior art. Thus, oxymetric measurements of the HbO.sub.2 saturation in the capillary area of the skin have been proposed. Another approach utilizes a measurement of the radioactivity of natural or radioactively identified test substances, for instance radioactively identified glucose. Still another approach measures blood gases which can diffuse through the skin or the organ surface to an electrode arrangement, for instance O.sub.2 and CO.sub.2.
These measurements, also, cannot indicate the perfusion efficiency factor because they are directed only to the local indicator concentration, and are not correlated with the rate of perfusion.